The invention relates to a method of and an arrangement for processing lengths of material.
More particularly, the invention relates to a method of and an arrangement for calendering lengths of material, e.g., bands of paper and the like.
A known arrangement for processing lengths of material has one or more hard or inelastic processing rollers which are advantageously capable of being heated. The arrangement further includes two or more elastically deformable working rollers each of which defines a gap with the processing roller or rollers. The material to be processed travels through the gaps. The working rollers are movably mounted and a moving mechanism is provided to move the working rollers between an operative position in which they are urged against the processing roller or rollers and an inoperative position in which they are spaced from the processing roller or rollers. The processing roller or rollers are rotated at a predetermined peripheral speed during processing and the working rollers may be accelerated to such speed by means of an adjustable drive mechanism. Guide elements guide the material in such a manner that the material does not contact a working roller which is in its inoperative position, i.e., the material contacts only the processing roller when passing through a gap defined by such roller and a working roller which is in its operative position.
U.S. Pat. No. 3,254,593 discloses a calender for paper which is directly connected to a paper processing machine. In the calender, the paper passes through two units each of which is made up of a processing roller and two diametrically opposite working rollers. The paper thus travels through and is compressed in four gaps. The processing rollers are heated and one side of the paper contacts the respective processing roller in the two upstream gaps while the other side of the paper contacts the respective processing roller in the two downstream gaps. The contact areas between the paper and the processing rollers vary. The working rollers are mounted in pivotable supports and pneumatic units are provided to move the working rollers from their inoperative positions to their operative positions and to bias the working rollers towards the processing rollers. The working rollers are driven by the shafts of the processing rollers via belt drives and movable or adjustable couplings. By switching on the belt drives and adjusting the couplings, the peripheral speeds of the working rollers may be at least approximately synchronized with the peripheral speeds of the processing rollers.
The processing rollers are designated as hard or inelastic since they have jackets or shells composed of steel, hard cast iron or another hard metallic material. The working rollers are designated as elastic or elastically deformable since they are coated with an elasto-viscous material, e.g., paper. The elastic working rollers are subjected to greater wear and are more prone to damage by the material being processed than the processing rollers.
Accordingly, the life of a working roller is substantially shorter than that of a processing roller. A conventional calender such as that described above must be stopped when a working roller becomes worn or damaged in order to permit replacement of the working roller. This involves a loss in production time ranging from 30 minutes to several hours. In addition, restarting of the calender entails costs which would otherwise not have been incurred.